The present invention relates to the general field of cooling devices for stationary rings surrounding flow paths for hot gas in gas turbines. It relates more particularly to a cooling device that makes it possible to channel and to use the air coming from leakage through the seals of the fasteners that fasten together the ring-forming segments and their supports.
In a gas turbine, e.g. in a high-pressure turbine of a turbomachine, the moving blades are surrounded by a stationary ring over the entire circumference of a stationary housing forming a shroud. The ring is generally in the form of sectors, i.e. it is made up of a plurality of ring segments that are placed end to end, and it contributes to defining the flow path for the hot gas coming from the combustion chamber of the turbomachine and passing through the turbine.
The ring segments are fastened onto the shroud by means of a stationary support-forming spacer that is likewise in the form of sectors made up of a plurality of spacer segments. More particularly, the ring segments are fastened onto the spacer segments by means of upstream and downstream fastener systems. In addition, the ring segments and the spacer segments are disposed relative to one another so as to form an annular “impact” cavity which is radially defined between axial annular walls of the spacer and ring segments.
It is known to provide such ring segments with cooling devices enabling them to withstand the high temperatures of the hot gas with which they are in contact. One of the methods of cooling the ring segments consists in forming a cooling-air supply orifice in each spacer segment so as to supply air to the impact cavity formed between the ring and spacer segments, and in forming a plurality of air exhaust holes in walls of the ring segments, said air exhaust holes opening out both into the cavity, and into the hot-gas flow path 6. An impact plate can also be disposed in the impact cavity between the air supply orifice and the air exhaust holes of the ring segments. Because of the pressure difference on each side of the impact plate, the air passes through said plate, impacts against the walls of the ring segments to be cooled, and is evacuated via the air exhaust holes pierced through said walls.
Such an arrangement generally enables the ring segments to be cooled effectively. However, in view of the significant difference in air pressure between the impact cavity and the hot-gas flow path, air leaks occur through the fastener systems that fasten the ring segments onto the spacer segments. These leaks result from the fastener systems being poorly sealed. In practice, the leaked air flows tangentially along a ring segment and is evacuated into the hot-gas flow path at the join between adjacent ring segments. This air, which can represent up to 0.2% of the total flow of cooling-air, does not participate in cooling the ring segments. This represents a significant quantity of air that is not used, and that could be used to cool other sectors of the turbomachine.